CIE IGCSE Chemistry Solved Past Paper Oct/Nov 2019 P41
1 ai) K+ ii) Cr3+ iii) Ca2+ iv) Br- v) SO4-
b) Place salt on nichrome wire,then heat using a bunsen flame
c) Mg3(PO4)2 (here valencies are crossed to write formula of the compound)
2a) Atoms of the same element with same number of protons but different number of neutrons
bi) 18 (34-16)
ii) By gaining 2 electrons
iii) Calcium (both have a total of 18 electrons)
ci) (l) + (g) —> (g)
ii) Vanadium(V)oxide, and 450? of temperature
iii) S03 +H2SO4——> H2S2O7
H2S2O7 + H2O——> 2H2SO4
di) It causes acid rain (by dissolving in rain water)
ii) Aqueous potassium manganate (Vll) turns from purple to colourless
e) a) Write symbols of elements:
Na S O
b) Calculate moles using mass or % composition given in the question: 29.1/23 40.5/32 30.4/16
= 1.265 1.266 1.9
c) Calculate ratio by dividing all moles with least value (1.265 here)
= (1 : 1: 1.5) *2 (multiply by 2 to obtain whole numbers)
= Na2S2O3
3a) They can all conduct electricity
b) Water, oxygen
ci) Zinc is more reactive than iron
ii) Fe3+, gains electron
d) Add hydrochloric acid, zinc oxide it dissolves, add sodium hydroxide, zinc oxide dissolves
4 ai) Cobalt carbonate
ii) Lead iodide
b) 2AgNO3 + Na2SO3——> Ag2CO3 + 2NaNO3
c) Pb2+ + 2I- —> PbI2
d) It removes carbonate ions
5 ai) Addition
ii) CH2 (simplest form)
bi) They have the same molecular formula but different structural formula
ii) Butane, propane with methyl group on second carbon in chain
iii) 2C4H10 + 9O2 8CO + 10H2O
6a) Moles = concentration*volume(in dim3)
= 0.18*(20/1000) = 0.0036 mol
2 mol of HCL give 1 mol of Na2CO3 from ratio set in equation. So 0.0036mol/2 = 0.0018 mol of Na2CO3
Concentration = moles/volume(in dm3)
= 0.0018/(25/1000)= 0.072mol/dm3
b) 0.0048/24 = 0.002mol
ci) Converting moles to mass
Mass = moles*molar mass
= 8.89*(1+80)= 720.09g/dm3
ii) Ions in aqueous form can move and carry charge
iii) It is reactive, could react with the products
iv) Bromine gas (more reactive than hydroxide ion,attracted towards positive electrode of opposite charge)
v) 2H+ + 2e- —–> H2
7a) C6H12O6—–> 2CO + 2C2H5OH
It requires yeast, 30 degrees Celsius of temperature and anaerobic conditions, separated by fractional distillation
b) 5(C-H) + C-C + C-O + O-H + 3(O=O)
(5*413)+ (347) + 358 + 464 + (3*498) = 4728
4(C=O) + 6(O-H)
(4*805) + (6*464) =6004
Energy change = 4728-6004 = -1276 kJ/mol
ci) It speeds up a chemical reaction without being used itself
ii) 2 carbon atoms share 2 electrons among them. 1 carbon atom shares 1 electron each with 3 hydrogen atoms. The 2nd remaining carbon atom shares one electron with hydrogen and the remaining two with oxygen and so forming a double bond.
iii) Weaker attractive forces in ethanol
di) Moves right because R.H.S has fewest number of molecules
ii) Rate of reaction increases as number of collisions per unit volume increase.
iii) Moves left, because backward reaction is endothermic.